1. Field of the Invention
The present invention relates to a vacuum valve for separating vacuum chambers. In particular the present invention relates to a vacuum valve including a valve body with a valve seat and a valve slide the closing member of which is provided with an elastomeric circumferentially closed seal which, in the closed condition of the vacuum valve, engages the sealing surface of the valve seat.
2. Description of the Prior Art
A vacuum valve for separating two vacuum chambers should meet different requirements than, e.g., a gas inlet valve or a valve provided between a vacuum chamber and a pump. The vacuum valve arranged between or separating two vacuum chambers is sometimes called a transfer valve. It should have a large through-opening, be able to be open or closed relatively quick, be suitable for a large number of openings and closings, and be suitable for application of a pressure difference to both of its sides. It is not necessary for the transfer valve to be able to open under application of a pressure difference thereto, though this is usual the case in many of conventional transfer valves. For opening the valve, both chambers can be brought under vacuum or, alternatively, both chambers can be flooded. If the possibility of a transfer valve to open, when one chamber is under vacuum and another chamber is flooded, is eliminated, the danger of operating errors is substantially reduced.
In vacuum valves with valve slides provided with elastomeric seals, it should be insured, during the displacement of the closing member into the valve closed position, that the seal is not stressed transverse to its longitudinal direction at the moment it contacts the sealing surface. The shear stresses acting on the seal secured on the closing member cause movement of the closing member transverse to the sealing surface, adversely affecting the function of the vacuum valve. Inevitable unevenness of the sealing surfaces, even when located in a microscopically small region, adversely affect sealing, resulting in that the slide, as applicable to vacuum technology, is not sealed any more. Microscopically small openings between the sealed from each other spaces are xe2x80x9cholesxe2x80x9d the size of which can exceed the size of gas molecules in several times.
In vacuum technology, the valve slide is so designed that the closing member, when moving into the closed position, is displaced substantially transverse to the sealing surface of the valve seat. E.g., German Publication DE 31 30 653A1 discloses a valve slide in which sealing plates, after the closing member has been displaced into its closed position, are pressed against the seals on the sealing surfaces by a toggle lever. Similar construction are also disclosed in German Publication DE 29 04 248 and in U.S. Pat. No. 3,262,672.
In another type of vacuum valves with valve slides, the sealing surfaces and the surfaces on which elastomeric seals are provided have a three-dimensional shape formed in such a way that upon displacement of the closing member into the closed position, no shear loads act on the elastomeric seal. The forces, which are applied to the seal, act either substantially in the direction transverse to the sealing surface or have also a force component acting in the longitudinal direction of the seal. By eliminating action on an elastomeric seal of forces, which cause a shear loading of the seal, during the closing displacement of the closing member, the distortion of the seal during a closing step is prevented to a most possible extent. This type of a vacuum valve with a valve slide is disclosed in German Publications DE 38 31 249A1 and DE 37 17 724 A1, German Patents Nos. 3,801,998; 3,831,249; and British Publication No. 2,045,898. In all of the vacuum valves disclosed in the above-listed Publications, a section of the seal lies on the front, viewed in the direction of the closing movement of the closing member, end section of the closing member. For sealing the valve, it is only necessary to apply a sealing force sufficient to deform the elastomeric seal. Usually, the applied sealing force amounts to at least 3 kg/cm with reference to a longitudinal extent of the circumferentially closed seal.
Transfer valves are used, e.g., in vacuum process plants or apparatuses used in semi-conductor industry. Such plants or apparatuses include, usually, a central handling chamber, in which a wafer is brought, and which is associated with different process chambers. In process chambers, the wafer is subjected to different processes during which process gases are pumped into or out of the process chambers. The process gases act on the elastomeric seals of the transfer valve, and the elastomeric seals, because of this, need be replaced from time to time. It was observed that the greater the elastomeric seals are subjected to the action of the process gases the stronger they become compressed.
Under normal operational conditions, a relatively small pressure difference exists between the central handling chamber and separate process chambers. In case of an accident or during cleaning of a process chamber, the transfer valve should be sealed against atmosphere.
Accordingly, an object of the present invention is to provide a transfer or vacuum valve with elastomeric seals suitable for use in an aggressive environment and having a longer service life than the conventionally used vacuum or transfer valves.
Another object of the present invention is to provide a transfer or vacuum valve which would not open under a pressure difference when only one side of the valve is subjected to vacuum.
A still further object of the present invention is to provide a transfer or vacuum valve that requires a small closing force for closing the valve.
These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a vacuum valve including a valve body having an opening an axial direction of which defines a flow direction of the valve, and a valve seat having two sealing surfaces encompassing the valve opening. The vacuum valve further includes a valve slide including a closing member displaceable transverse to the flow direction of the valve and having two wedge-shaped, tapering toward each other side surfaces, and elastomeric, circumferentially closed seals provided on the side surfaces of the closing member. Respective sealing surfaces of the valve seat and respective side surfaces of the closing member extend parallel to each other and form, over their entire extent, with the flow direction of the valve an angle greater than 45xc2x0.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.